Parents Helping Parents has a Resource Directory where you can search for advocates and attorneys. Go to http://www.php.com/resources for the PHP Resource Directory. On the right hand side, there is box with Services which includes links for Advocates and Attorneys.

Also, COPAA (Council of Parent Attorneys and Advocates) maintains a database of advocates and attorneys. Go to http://www.copaa.org/find/index.php for their website.